...does it have a small number stamped on the back-case? I have a Timex 100 with "09T95" on the back, which would indicate the year 1959 ( I, with others, think - this is just speculation - that the two last digits indicate the year, but written backwards... ). If your watch has no number it is propably stamped with ink on the inside of the back-case. I guess you have the two-piece screw-on back, and you are able to remove it with a small screwdriver - there should be 4 slots in the back-case outer ring. Or, you could try with your thumbnails - I have tried that a few times, and if the case isn't too tight it will work!
As for more info on the Timex 100: it runs with the Timex 22 movement - a very sturdy movement. To be honest I don't know what the difference between the Marlin and the 100 is. Maybe the size? The 100 is quite big for the period. It also has the little "teardrop" at the short end of the seconds hand. Hopefully someone else here will know more.